1. Field of the Invention
The present invention relates to a write current setting method, and, in particular, to a write current setting method and a write current setting apparatus for setting an optimum write current for an information storing device in which the characteristics of a write head change in accordance with the temperature. The present invention also relates to the information storing device.
Recently, miniaturization and larger capacity are required for an external information storing device. For this purpose, increasing the information storing density and increasing the information transfer speed are required for a magnetic disk device.
In the magnetic disk device, to increase the information storing density, the track width on the magnetic disk is greatly narrowed. As a result of the track width being narrowed, crosstalk between adjacent tracks becomes a problem.
Further, in order to increase information transfer speed, the write frequency is increased. Thereby, magnetization of the magnetic disk is insufficient. As a result, when new information is overwritten onto the magnetic disk, it is likely that old information still remains on the magnetic disk. In addition, the overwrite capability is degraded when crosstalk is reduced, and crosstalk increases when the overwrite capability is improved. It is necessary to set a write current such that the balance between a reduction of crosstalk and an improvement of write capability is optimum when the write current is used.
2. Description of the Related Art
FIG. 1 shows a plan view of an example of a magnetic disk device in the related art. In the magnetic disk device 11 shown in FIG. 1, an actuator 12 is provided with arms 13. A supporting spring mechanism 13a is provided to the extending end of each arm 13. Each arm 13 is provided with a magnetic head 14 at the extending end thereof. A base portion of the arms 13 is rotatably supported by a pivot 15. The arms 13 are positioned between adjacent ones of a plurality of magnetic disks 20 which will be described later.
A coil supporting portion 16 is provided at the side opposite to the arm 13 with respect to the pivot 15. A coil 17 is wound on the coil supporting portion 16. Two magnets 18a and 18b are fixed below the coil 17. The coil 17 and magnets 18a, 18b form a VCM (Voice Coil Motor).
In the magnetic disk device 11, the plurality of magnetic disks 20 are fixed to a spindle motor and are rotated by the spindle motor. The arm 13 is rotated as a result of a current being supplied to the coil 17 from a wiring board 21 via a flexible printed board 22. Thereby, with respect to these magnetic disks 20, the arms 13 are rotated so that each magnetic head 14 moves in a radial direction of the magnetic disks 20.
As each magnetic head 14, a thin-film head is used, and the magnetic heads 14 float by a predetermined amount due to the rotation of the magnetic disks 20, respectively. Each thin-film magnetic head 14 includes a write head formed as a result of forming a coil and a magnetic gap in a thin-film formation technique, and is formed on a slider. Each thin-film magnetic head 14 further includes a read head using a magneto-resistive device and is also formed on the slider. A predetermined current (write current) is supplied to the coil of the write head. Thereby, writing data to the respective magnetic disk 20 is performed through leakage magnetic flux occurring from converting electricity to magnetic flux. The data written on the magnetic disk is read through the read head and a waveform corresponding to the write current (amplitude of a read current) is obtained.
In the above-described magnetic disk device, because of increase of the information storing density, the track width on each magnetic disk 20 is greatly narrowed. As a result of the track width being narrowed, crosstalk between adjacent tracks becomes a problem. Further, in order to increase the information storing density and to increase information transfer speed, the write frequency is increased. As a result, when new information is overwritten onto the magnetic disk 20, it is likely that old information still remains on the magnetic disk 20. Thus, problematically, the overwrite capability is degraded.
As mentioned above, the overwrite capability is degraded when crosstalk is reduced, and crosstalk increases when the overwrite capability is improved. Therefore, it is necessary to set the write current carefully.
Further, the intensity of magnetization of the magnetic disk changes when the ambient temperature changes. Accordingly, it is necessary to change the write current so that both the crosstalk reduction and the overwrite capability improvement are at adequate levels for each temperature.
Characteristics of a magnetic disk device will be described.
FIGS. 2A, 2B and 2C show various characteristics of the magnetic disk device. FIG. 2A shows characteristics of crosstalk with respect to overwrite (O/W) gains. FIG. 2B shows characteristics of overwrite (O/W) gains with respect to temperatures. FIG. 2C shows characteristics of overwrite (O/W) gains with respect to write currents.
In the magnetic disk device having the characteristics shown in FIGS. 2A, 2B and 2C, as shown in FIG. 2A, in order to make crosstalk be on the order of -30 dB, it is necessary to controls the overwrite (O/W) gain to on the order of -30 dB.
Further, as shown in FIG. 2B, by changing the write current Iw, from 35 mA, to 30 mA, and to 25 mA, in response to rise of the temperature, it is possible to maintain the overwrite (O/W) gain to -30 dB.
Further, as shown in FIG. 2C, the overwrite (O/W) characteristics with respect to the write current Iw vary among magnetic heads 14-1, 14-2, 14-3 and 14-4, one of which is mounted to the magnetic disk device. Accordingly, by differently controlling the write current Iw for particular heads 14-1, 14-2, 14-3 and 14-4, it is possible to maintain the overwrite (O/W) gain to -30 dB.
Japanese Laid-Open Patent Application Nos. 63-167404, 1-245406 and 1-317208 proposed methods for setting the write current in accordance with the temperature in magnetic disk devices.
In these arts, a temperature sensor and a table in which the optimum write currents are set for particular temperatures are provided inside a magnetic disk device. Thereby, the write current is controlled in accordance with the detected temperature of the temperature sensor. Thus, information can be written in a disk independent of the temperature. In these arts, the overwrite characteristics are measured and the optimum write currents are set.
However, in the write current setting methods for magnetic disk devices in the related art, the overwrite characteristics themselves are measured. When the overwrite characteristics are measured, it is necessary to directly measure the state of the magnetic disk. Therefore, the measurement cannot be performed after the magnetic disk device has been assembled. Further, a considerable time is required for the measurement.